STRUCTURE OF CORAL ISLANDS. 175 



the eastern and western ranges of land in this Great Bank is 

 really analogous to that of the opposite sides of the great Mal- 

 dive Atoll Group. The remaining islands and reefs are mostly 

 isolated. In the triangular interval between the Great Bahama 

 Bank, Florida and Cuba, lies the reef called Salt Key Bank. 

 The northern coast of Cuba, south of this bank, and to the 

 eastward, is bordered by coral reefs. 



The following are notes from an abstract of a paper pre- 

 sented to the Geological Society in 1852, by Major-General 

 R. J. Nelson, R.E., and published in the Quarterly Journal of 

 the Society for 1853, p. 200 : — 



" The loftiest land in the Bahamas, according to the maps of 

 the Hydrographical Office, is only 230 feet above the sea. 

 Generally speaking, the hills on the larger islands are much 

 under 100 feet in height, and on the islets from 50 to 10 feet. 



The surface generally is occupied by low rocky 



hills, either surrounding basins or forming parts of what may 

 once have been basins, and rarely by distinct hill and valley of 

 the ordinary character. The bottoms of these basins are 

 usually flat and rocky, only a few inches above the average 

 high-water level, and have a rough and cavernous surface. 

 Water, more or less brackish, rises and falls everywhere 

 throughout the lower parts of these flats, though not contem- 

 poraneously with the tide,^ or at a uniform rate. The surface 

 is sometimes covered with grass and low bush, and sometimes 

 it consists of the bare rock, full of hollows, which are coated 

 or even arched over with sub-stalagmitic substance. It is in 

 these cavities, locally termed ' pot-holes,' that most of the soil 

 is found ; and in the gardens made on such ground, fruit-trees, 

 pine-apples, Indian corn, sugar-cane, &c., grow luxuriantly. 

 Besides these ' rock-marshes ' there are also ordinary marshes 

 and mangrove swamps, of no great extent or depth, which are 

 more or less in connection with the sea. On the larger islands 

 the rocky surface of the hills is very thinly and partially 

 covered with ' red earth,' mixed in varying proportions with 



* At Nassau, Bahamas, the tide rises from 4 to 3 feet (spring to neap) ; 

 but at Bermuda it rises from 6 to 42. 



